In the dressing of animal carcasses, typically of pork, but also of other animals, the carcass is separated down the back bone into two halves. The loin portion of the carcass which is usually one of the more desirable portions of the carcass then consists of a portion of back bone, and ribs, and meat, and an outer layer of fat. It is the practice when dressing carcasses to separate the so-called "back fat" from the loin meat or lean portion. In the past, this was usually done by hand. In U.S. Pat. No. 4,189,806, there is described a machine for mechanical separation of back fat from the loin. In this machine, the loin is supported on a conveyor with an arcuate cross-section, and is subjected to pressure from overhead pressure means. A curved knife blade is placed in the path of the loin, between the lower conveyor and the upper pressure means. The loin is thus forced against the blade, and the back fat is separated or trimmed away from the meat, by the curved knife blade.
This machine was a considerable improvement upon machines which had been proposed earlier, for the same purpose. However, there were certain shortcomings. Obviously, carcasses of different weights, strains and sub-species will have more or less back fat and meat. The location of the knife blade must then be capable of being adjustable, to provide the optimum degree of trimming. However, in order to speed up processing time, it is desirable to process loins through the machine on a more or less continuous basis. It is, therefore, sometimes attempted to effect a manual adjustment of the position of the blade for each portion of the loin but this can be erratic. In the machine, as described in the aforesaid patent, it was, in practice usually necessary to adjust the blade to an average position, and accept some degree either of wastage of meat, or of excess fat being left on the meat.
In addition, the passing of a knife blade through a layer of fat, inevitably results in a deposit of fat on the knife blade which gradually builds up. As the fat deposit builds up, the knife blade presents more and more frictional resistance to passage of the loin. As a result, the motive power required to force the loin past the knife blade increases, to the point where it eventually becomes necessary to stop the machine and clean the knife blade. Again, this interrupts processing and slows down the entire line.